Vapor cells or atomic vapor cells are used in the construction of atomic clocks, magnetometers, and other devices, and allow chip-scale structures with significant power consumption advantages for use in portable battery-powered devices over conventional atomic clocks. Ideally, an alkali metal gas such as Cesium (Cs) or Rubidium (Rb) is provided within a sealed cavity and a light source optically excites the alkali metal, with the frequency of electronic transition of an alkali atom having a single electron in the outer shell being used as an absolute frequency reference for generating highly accurate clock signals. Optical interrogation at different frequencies within a frequency band can be used to identify a transition frequency through absorption spectrum detection to provide an absolute frequency reference for a clock. Proper operation for atomic clock or other applications is facilitated by a clear unobstructed optical path through the vapor cell. One method of adding a controlled amount of Cs to a vapor cell is to introduce aqueous Cesium Azide (CsN3) into the cell and then allow the water to evaporate leaving solid CsN3 residue. After the vapor cell is sealed, UV photolysis is carried out to dissociate the CsN3 residue into Cs and N2. However, conventional vapor cell fabrication techniques suffer from formation of residual alkali metal azide on the lower cell window, causing undesirable absorption and/or scattering of light during cell operation. Such CsN3 or other alkali metal solids, moreover, cannot be removed from the vapor cell window by post-processing. Accordingly, a need remains for vapor cells with unobstructed optical paths for efficient identification of the alkali metal electronic transmission frequency for atomic clocks and other applications.